1. Field of the Invention
The present invention relates to a method of establishing link, and more particularly, to a method of establishing link for handover by a multi-mode mobile terminal.
2. Discussion of the Related Art
In a IEEE 802.21, discussions related to a Media Independent Handover (MIH) are actively taking place. In particular, discussions related to providing seamless handover and service continuity between heterogeneous networks are increasing. Among the topics of discussions are function of the MIH, an Event Service (ES), Command Service (CS), and Information Service (IS).
A mobile terminal is multi modal which supports at least one interface type, and the interface types can be any one of the following. The interface types include a wire-line type similar an Ethernet of IEEE 802.3, a wireless interfaces based on IEEE 802.xx (e.g., 802.11, 802.15, 802.16), and an interface defined by a cellular standard organization (e.g., 3rd Generation Partnership Program (3GPP), 3rd Generation Partnership Program 2 (3GPP2)).
The MIH is defined between the IEEE 802 series interfaces or between the IEEE802 series interfaces and non-IEEE 802 series interfaces (e.g., 3GPP, 3GPP2). Furthermore, the MIH has to be supported by upper layer mobile support protocol such as a Mobile Internet Protocol (Mobile IP) and a Session Initiation Protocol (SIP) in order to provide seamless handover and uninterrupted service.
FIG. 1 illustrates a multi-mode mobile terminal. The mobile terminal comprises a wired Local Area Network (LAN), a wireless LAN, a broadband radio access network, and a cellular network. As illustrated in FIG. 1, the mobile terminal comprises a Physical (PHY) layer and a Medium Access Control (MAC) layer associated with each mode and has the MIH Function located below an Internet Protocol (IP) layer. The MIH function facilitates the handover process by using the input values from Layer 2 such as trigger event information and information of other networks. Moreover, the MIH Function can include input values (e.g., user policy and configuration) which can affect the handover procedure. In addition, general interfaces (e.g., the Mobile IP and the SIP) are defined between Layer 3 entities and the MIH Function. These interfaces provide information associated with Layer 1 (i.e., PHY Layer) and Layer 2 (i.e., MAC Layer) as well as mobility management. The MIH Function provides services to the upper layers through a single technology-independent interface and obtains services from the lower layers through a variety of technology-dependent interfaces. The MIH uses the ES and the IS to acquire information on lower layer and the network.
Furthermore, an upper management entity, located in the upper layer to monitor and control statuses of various links of the mobile terminal, is used to perform handover control function and device manager function. Here, the handover control function and the device manager can be independently located or can be included in the upper management entity. The terms upper layer and higher layer can be used interchangeably.
FIG. 2 illustrates a mobile terminal having a MIH Function and a network having a functional entity and transmission protocol. In FIG. 2, the dotted lines represent services such as a primitive and the ES. As illustrated in FIG. 2, the network layer uses the information from a link layer in order to quickly re-establish connection. The link layer event can be used to predict the user's movement and also can be used prepare for handover between the mobile terminal and the network. The trigger for handover procedure can be initiated from the PHY layer and the MAC layer. Moreover, the source of the trigger can be a local stack or a remote stack.
FIG. 3 illustrates an Event Service when performing handover to a new link. More specifically, FIG. 3 illustrates the ES related to establishing a new link due to decreased quality of the currently connected link.
A Command Service (CS) refers to the commands sent from the higher layers to the lower layers, including commands sent from the higher layers to the MIH or from the MIH to the lower layers. These commands are used to deliver higher layer decisions to lower layer as well as to control the activities of the lower layer entities.
An Information Service (IS) provides a framework by which a MIH Function both in the mobile terminal and in the network can discover and obtain network information within a geographical area to facilitate handovers. Here, the IS is accessible to any network. The IS includes the following information elements, such as a link access parameter, a security mechanism, a neighbor map, a location, a cost of link, and a provider and other access information.
When performing handover procedure in heterogeneous or homogeneous networks, referring to FIG. 3, the multi-mode mobile terminal first performs scanning to discover accessible link. Upon discovering the link to access, the mobile terminal delivers Link_Available trigger to the upper management entity and performs a link selection procedure to select one link from a plurality of accessible links. The upper management entity delivers the selected link to allow the MIH to establish connection with the corresponding link. However, according to the conventional trigger, the process of establishing connection with the selected link cannot be accomplished.